1. Field of the Invention
The present invention relates to an image reading apparatus, and an image forming apparatus having an apparatus body including the image reading apparatus.
2. Description of the Related Art
FIG. 8 is a schematic cross-sectional view taken along a moving direction K1 of a carriage 807 of an image reading apparatus 800 according to a comparative example. Light L emitted from an LED 801 of the carriage 807 passes through a light guide member 802 and illuminates a document surface (image surface) Gf of a document G placed on a fixed reading glass 803. The carriage 807 reads a two-dimensional image of the document surface Gf through line reading in a main scanning direction orthogonal to the moving direction K1 and movement in a sub-scanning direction that is the moving direction K1. The light L reflected from the document surface Gf is further reflected by a plurality of reflecting mirrors 804, and forms an image on a photoelectric conversion element 806 by an imaging optical unit 805. Then, the light L is converted into an electrical signal.
In general, the light L emitted from the LED 801 has such a light distribution characteristic that the light is bright at a center and becomes darker in positions away from the center. A light intensity obtained when only one LED 801 is used as a light source to illuminate the document is not sufficient to illuminate the document. Therefore, a plurality of LEDs 801 is necessary. A portion including the LEDs 801 and the light guide member 802 serves as a document illumination unit 808.
There is such an image reading apparatus that, when the LEDs 801 in the document illumination unit 808 are used as a light source for document illumination, the plurality of LEDs are arranged in an array form to prevent degradation of a peripheral light intensity due to the imaging optical unit 805 and this arrangement has been devised (Japanese Patent Application Laid-Open No. S61-142857).
In this image reading apparatus, a large number of light emitting elements are arranged in a main scanning direction, and at least one of an emission intensity of each light emitting element and an arrangement pitch between the light emitting elements is changed so that an intensity of irradiation light from both end portions in the main scanning direction is larger than that from a central portion in the main scanning direction. As a result, in the image reading apparatus, a cosine-fourth-law characteristic of an imaging lens is corrected in an illuminance distribution on a document irradiation surface in advance.
In the image reading apparatus according to the comparative example, there is a problem in that, when the fixed reading glass 803 serving as a transparent member is deflected in a direction approaching the carriage 807, the illuminance is insufficient and uneven, and the entire document cannot be read with uniform reading precision.
As illustrated in FIG. 9, when a document GB having a great thickness and a binding portion, such as papers or a book, is placed on the fixed reading glass 803 by a user, there is a gap C between the document GB and the fixed reading glass 803. In order to reduce the gap C, the user strongly presses the document GB against the fixed reading glass 803 through intermediation of a pressing plate 847 for covering the fixed reading glass 803 (in a direction indicated by an arrow W). Then, a pressed portion of the fixed reading glass 803 may be elastically deformed downward from a flat position indicated by a solid line and may be deflected as indicated by a dashed line. When the fixed reading glass 803 is deflected downward, the distance between the fixed reading glass 803 and the carriage 807 is not uniform. Therefore, in the image reading apparatus according to the comparative example, there is a problem in that the illuminance is insufficient and uneven, and the entire document cannot be read with uniform reading precision.
Further, an image forming apparatus having an apparatus body including such an image reading apparatus has a problem in that a high-quality image cannot be formed.